From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 85F1BC433DB for ; Thu, 28 Jan 2021 19:30:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2EC3864E2C for ; Thu, 28 Jan 2021 19:30:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232054AbhA1SuB (ORCPT ); Thu, 28 Jan 2021 13:50:01 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:34057 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232285AbhA1SqO (ORCPT ); Thu, 28 Jan 2021 13:46:14 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611859487; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=09rgXsilTnae6yAI2+7X50tmB4yjigjLFKTbsUMux9E=; b=bvYmjmb1DmlKtjx6Prm5RVb3Wl3u7ivb/AOOOnIaRVJvcb0Amn9kdSHxYzBgWMrLyeaktg 0iV/4svvQjBLaYcVMkSL41fXbAUvt3UunRcB9Ly9/M/6kxPMFYf0E+sBM3buKxadZpoiTB vvto6lbSvpefzFi6YZzqm8QPoITyEMw= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-214-CUuh-d1UNh2BVbeJQyxPzQ-1; Thu, 28 Jan 2021 13:44:45 -0500 X-MC-Unique: CUuh-d1UNh2BVbeJQyxPzQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E71408144E2; Thu, 28 Jan 2021 18:44:42 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B06D36085D; Thu, 28 Jan 2021 18:44:42 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id E45104178900; Thu, 28 Jan 2021 15:44:20 -0300 (-03) Message-ID: <20210128184346.748987586@fuller.cnet> User-Agent: quilt/0.66 Date: Thu, 28 Jan 2021 15:40:49 -0300 From: Marcelo Tosatti To: Peter Zijlstra , Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Marcelo Tosatti Subject: [patch 1/3] nohz: only wakeup a single target cpu when kicking a task References: <20210128184048.287626221@fuller.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When adding a tick dependency to a task, its necessary to wakeup the CPU where the task resides to reevaluate tick dependencies on that CPU. However the current code wakes up all nohz_full CPUs, which is unnecessary. Switch to waking up a single CPU, by using ordering of writes to task->cpu and task->tick_dep_mask. From: Frederic Weisbecker Suggested-by: Peter Zijlstra Signed-off-by: Frederic Weisbecker Signed-off-by: Marcelo Tosatti Index: linux-2.6/kernel/time/tick-sched.c =================================================================== --- linux-2.6.orig/kernel/time/tick-sched.c +++ linux-2.6/kernel/time/tick-sched.c @@ -322,6 +322,31 @@ void tick_nohz_full_kick_cpu(int cpu) irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); } +static void tick_nohz_kick_task(struct task_struct *tsk) +{ + int cpu = task_cpu(tsk); + + /* + * If the task concurrently migrates to another cpu, + * we guarantee it sees the new tick dependency upon + * schedule. + * + * + * set_task_cpu(p, cpu); + * STORE p->cpu = @cpu + * __schedule() (switch to task 'p') + * LOCK rq->lock + * smp_mb__after_spin_lock() STORE p->tick_dep_mask + * tick_nohz_task_switch() smp_mb() (atomic_fetch_or()) + * LOAD p->tick_dep_mask LOAD p->cpu + */ + + preempt_disable(); + if (cpu_online(cpu)) + tick_nohz_full_kick_cpu(cpu); + preempt_enable(); +} + /* * Kick all full dynticks CPUs in order to force these to re-evaluate * their dependency on the tick and restart it if necessary. @@ -404,19 +429,8 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cp */ void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) { - if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) { - if (tsk == current) { - preempt_disable(); - tick_nohz_full_kick(); - preempt_enable(); - } else { - /* - * Some future tick_nohz_full_kick_task() - * should optimize this. - */ - tick_nohz_full_kick_all(); - } - } + if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) + tick_nohz_kick_task(tsk); } EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task);